KONNA, Mali/PARIS Jan 26 (Reuters) - French and Malianforces fighting Islamist rebels took control on Saturday of therebel bastion of Gao, the biggest military success so far in anoffensive against al Qaeda-allied insurgents occupying thecountry's north.

The United States and Europe back the U.N.-mandated Malioperation as a counterstrike against the threat of radicalIslamist jihadists using the West African state's inhospitableSahara desert as a launching pad for international attacks.

In an overnight assault on Gao backed by French warplanesand helicopters, French special forces seized the town's airportand a key bridge over the River Niger, killing an estimateddozen Islamist fighters without suffering any losses orinjuries, the French army said.

"The Malian army and the French control Gao today," Malianarmy spokesman Lieutenant Diaran Kone told Reuters.

The speed of the French action in a two-week-old campaignsuggested French and Malian government troops intended to driveaggressively into the north of Mali in the next few days againstother Islamist rebel strongholds, such as Timbuktu and Kidal.

There have been 30 French air strikes on militant targetsaround Gao and Timbuktu in the past 36 hours.

News that the French and Malian troops were at Gao, thelargest northern town held by the Islamists, came as Africanstates struggled to deploy their intervention force in Mali,known as AFISMA, under a U.N. mandate.

Regional army chiefs said on Saturday that a total of 7,700African soldiers would be dispatched, up from 5,700.

Liberia, Guinea-Bissau, Burundi, Guinea and Uganda are dueto join the mission but it was not clear if progress had beenmade at meetings in Abidjan or Addis Ababa to overcome gaps intransport, equipment and financing.

French army spokesman Colonel Thierry Burkhard said Frenchforces had come under fire from rebel fighters inside Gao, butthat both the bridge and airport runway were undamaged.

In Paris, the French defence ministry said Malian and Frenchtroop reinforcements were brought in and that soldiers from Chadand Niger, who have experience in desert warfare, were alsoflown in.

These Malian and regional troops would have the task ofsecuring Gao and its surrounding area, the ministry said.

To the west, French forces recaptured Lere, on the road toTimbuktu, and were advancing, a Malian military source said,asking not be named.

For two weeks, French jets and helicopter gunships have beenharrying the retreating Islamists, attacking their vehicles,command posts and weapons depots. The French action had stymieda sudden Islamist offensive launched in early January that hadthreatened Bamako, Mali's capital in the south of the country.

Reacting to the French-led offensive, one of the leaders ofthe alliance of Islamist groups occupying Mali's north promisedresistance to what he called the "new Crusader aggression", incomments published by Al Jazeera's Arabic website.

Yahya Abu Al-Hamman, leader in the Sahel of al Qaeda's NorthAfrican wing AQIM, which along with Malian militant group AnsarDine and AQIM splinter MUJWA occupies Mali's north, said a"Jihadist Islamist emirate" would be created in the territory.

Washington and European governments, while providing airliftand intelligence support to the anti-militant offensive in Mali,are not planning to send in any combat troops.

FRANCE TAKING THE LEAD

At an African Union summit in Addis Ababa, AU leaders calledon the United Nations to provide emergency logistics and fundingto allow the African force for Mali to deploy.

There appeared to be some embarrassment among Africanministers and leaders that the continent was having to rely on aformer colonial power, France, much criticised for past meddlingin Africa, to take the lead in the military campaign in Mali.